This invention relates generally to a method for fabricating a fully integrated (monolithic) inkjet printhead, and more particularly to a method for forming pillars within the printhead to reduce particle clogging of ink refill channels.
A thermal inkjet printhead is part of an inkjet pen. The inkjet pen typically includes a reservoir for storing ink, a casing and the inkjet printhead. The printhead includes a plurality of nozzles for ejecting ink. A nozzle operates by rapidly heating a small volume of ink in a nozzle chamber. The heating causes the ink to vaporize and be ejected through an orifice onto a print medium, (e.g., a sheet of paper). Properly sequenced ejection of ink from numerous nozzles arranged in a pattern causes characters, symbols or other graphics to be printed on the print medium as the printhead moves relative to the print medium.
The inkjet printhead includes one or more refill channels for carrying ink from the reservoir into respective nozzle chambers. According to one conventional fabrication methodology, a nozzle chamber is defined in a barrier layer applied to a substrate. An orifice plate is applied to the barrier layer. The substrate forms a floor of the firing chamber (along with a firing resistor), while the orifice plate forms a ceiling to the firing chamber. According to another conventional fabrication methodology, a fully integrated, or monolithic, printhead of inkjet nozzles is formed using photoimaging techniques similar to those used in semiconductor device manufacturing. The fully integrated thermal (FIT) inkjet printhead includes a thin film layer formed of various passivation, insulation, resistive and conductive layers applied to a silicon wafer.
One problem which affects print quality is clogging of the ink refill channels. Once a nozzle chamber is fired ejecting a drop of ink, ink flows from the reservoir through the ink refill channels into the nozzle chambers. Typically, the ink is stored within a porous material filling the reservoir to achieve fluid retention and fluid pressure benefits. A disadvantage of the porous material, however, is that particles are occasionally disengaged and carried by the ink into the ink refill channels. Even for devices without a porous material in the ink reservoir, particles remaining from manufacturing processes may be carried by ink to the refill channels. Such porous material particles or leftover manufacturing process particles can become lodged and block a refill channel. Blocking of a refill channel can cause premature failure of an inkjet firing chamber, or cause ink starvation of the inkjet firing chamber. The failure of a nozzle to eject an ink droplet can harm print quality. Redundant nozzles have been proposed and implemented as one solution to this problem.
Pillars and barrier islands have been proposed to capture particles and provide redundant pathways leading to the nozzle chambers. U.S. Pat. No. 5, 463,413 issued Oct. 31, 1995 to Ho et al. for "Internal support for Top-Shooter Thermal lnkjet Printhead" discloses pillars for a printhead formed by a substrate, barrier layer and orifice plate. U.S. Pat. No. 5,734,399 issued Mar. 31, 1998 to Weber et al. for "Particle Tolerant Inkjet Printhead Architecture" discloses barrier islands for a printhead also formed by a substrate, barrier layer and orifice plate. Both of these patents disclose forming the pillars or barrier islands in the barrier layer before applying the orifice plate.